Color separation scanners are well known and are operative to scan two dimensional color pictures, such as prints or transparencies, and to produce electrical signals which represent color separations thereof for subsequent use in process color printing.
Conventional scanners, such as those manufactured and sold by Hell of Germany and Dainippon Screen Seizo of Japan, typically employ a rotating drum onto which the two dimensional color picture is mounted. The drum rotates past a scanning head, which may comprise a CCD array, as taught in U.S. Pat. No. 4,256,969. According to that patent, a separate scan is carried out for each separation.
Various techniques are presently known for color separation in array detector based systems. One technique employs three primary Red, Green, and Blue filters installed over the scanning head of a single CCD linear or area array. A color picture can be constructed by repeatedly scanning the picture, each time with a different filter.
A second technique employs three colored fluorescent lamps. The picture is repeatedly scanned, each time under the illumination of a different lamp.
A third technique employs three sensors and dichroic mirrors or filters for separating the three elements of color, each of which is detected by a separate sensor. In its current state of the art, this third technique has not achieved pictures of a high enough quality to fulfill the requirements of pre-press processing.
Another technique employs a single CCD chip including three linear arrays, each having deposited thereon a different color filter. Lines are read in three colors and combined using electronic hardware. A delay of several lines is interposed between the lines read in the different colors.
Summarizing the state of the prior art, it can be said generally that the prior art scanners are relatively slow in operation and do not provide a capability for picture modification and adjustment at the scanning stage. All such image modification, rotation, cropping, adjustment and enhancement must be carried out once the scanned picture is stored in a computer memory, rendering such steps time-consuming and relatively expensive.